The invention relates, generally, to a touch input device and, more particularly, to an opto-matrix frame having digital ambient light compensation.
Coincident with the use of video displays has always been the problem of the man/machine interface. Traditionally, control of displayed information or cursors has been via a keyboard. Recently, however, a number of devices have been introduced which allow an operator to directly interact with the video display. These types of devices have included light pens, desk-type mouse controllers, or touch input devices such as a switch matrix or opto-electronic matrices. While generally switch-type overlays which are placed adjacent a video display are inexpensive to apply and utilize, they are generally susceptible to contact wear as well as distortion of the video information which is presented to the viewer, particularly in high usage environments. However, since opto-matrix schemes utilize light, which is generally in the infrared region, the switch matrix presented by the light beams is invisible to the viewer and, therefore, does not distort the video information displayed to the viewer and is not subject to wear in high usage environments. A number of schemes which utilize opto-matrix frames may be found in U.S. Pat. No. 4,267,443 "Photoelectric Input Apparatus", issued May 12, 1981 to Carroll et al.; U.S. Pat. No. 4,243,879 "Touch Panel with Ambient Light Sampling", issued Jan. 6, 1981 to Carroll et al.; U.S. Pat. No. 3,764,813 "Coordinate Detection System", issued Oct. 9, 1973 to Clement et al. These three schemes address problems inherent with opto-matrix devices such as increasing frame resolution without a corresponding increase in components, surrounding or ambient light compensation, or optimization of emitter/detector driving and detecting networks respectively. These systems still have drawbacks in some areas such as large component usage thereby resulting in higher costs, ambient light sensing which is based on a predetermined value rather than dynamically, and difficulty in compensating for reflection or glare which may result in stylii hits not being recorded.
Glare problems generally occur when an emitter is adjacent the corner of the frame or bezel such that light produced by the emitter bounces off an adjacent surface and is then detected by the detector such that any stylus which is introduced to the video display inherently blocks the majority of the light received by the detector but the reflectant light is sufficiently high for the detector and its associated circuitry to not perceive a hit. Accordingly, it is desirable to have a device which minimizes the number of components necessary for addressing and detecting emitters and detectors. Further, it is also desirable to have a device which dynamically compensates for ambient light and for variations in emitter output and detector sensitivity. Also, it is desirable to have a device which minimizes glare problems. Such a scheme is taught in the present invention.
It is a principal object of the invention to provide a touch input device comprising a four-sided frame, optical emitters disposed in two adjacent sides of the frame, optical detectors disposed in the two sides of the frame opposite the emitters, a sampling device for sequentially sampling the light received by the detectors, a converter device for converting the value of the light received by the detectors to a digital value, and a processor connected to the converter for comparing the output of the detector prior to and/or during and after energization of a corresponding emitter, thereby deriving a signal manifesting the interruption or noninterruption of light produced by the emitter and introduced to the detector regardless of ambient light as well as for a comparison threshold for subsequent detector samplings.